1. Field of the Invention
The present invention relates to storage batteries of the lead-acid type, and has particular application to a new type of organic expander composition which is incorporated into the oxide or paste used in making the negative plates of such storage batteries. The composition of the invention improves a storage battery by greatly increasing its capacity and life, particularly cycle life and cold cranking capacity at high rates of discharge and at low temperatures.
2. Description of the Related Art
As used herein, the term xe2x80x9coxyligninxe2x80x9d is defined as a chemical compound consisting principally of lignin derivatives in an oxidized state. Commercial examples are available under the tradenames Vanisperse A, an oxylignin produced by Borregaard LignoTech in Sarpsborg, Norway, Marasperse XC-2 an oxylignin produced by LignoTech USA, Inc. (a member of the Borregaard Group) in Rothschild, Wis., and Vanillex, an oxylignin produced by DP and Chemical Division of Nippon Paper Industries Co., Ltd., Tokyo Japan. These oxylignins are characterized as acid-insoluble and alkaline-dispersible lignin sulfonic acid compounds substantially free of calcium and manganese compounds as well as non-ligneous organic and inorganic impurities. These products are produced by treatment of softwood sulfite liquor under alkaline conditions at high temperature and high pressure. The treatment comprises a material reduction in the organically combined sulfur content, as well as condensation, cleavage and rearrangement reactions due to oxidation and hydrolysis. The reactions increase the number of phenolic and hydroxyl groups in the molecular structure. An example of a process for making these oxylignin compounds is described in U.S. Pat. No. 2,371,136 by Carlyle Harmon of Marathon Corporation, a predecessor of LignoTech USA, Inc. In the present art, the material described in U.S. Pat. No. 2,371,136 is referred to as an xe2x80x9coxyligninxe2x80x9d. The oxylignin, Vanisperse A, is the most widely used organic expander in storage batteries of the lead-acid type for starting, lighting and ignition (SLI) applications. Hence, Vanisperse A is the industry standard for organic expanders.
The term xe2x80x9ckraftxe2x80x9d lignin refers to lignin products derived from the alkaline pulping process by lowering the pH of the lignin solution. Then, by means of thorough washing a very pure lignin is obtained. Kraft lignin is also called sulfate or alkali lignin. In U.S. Pat. No. 4,293,459, it is stated that alkali or Kraft lignins are generally prepared by cooking woodchips with a 10% solution of a mixture of sodium hydroxide with about 20 mole percent of sodium sulfide resulting in a sodium modified compound which is very soluble in the strongly alkaline solutions. The alkali lignins are removed from solution by lowering the pH to the acid side whereby the alkali lignins precipitate. These precipitated unsulfonated, alkali lignins may be utilized to prepare sulfonated derivatives, typically by treating them with a solution of alkali sulfite or alkali sulfite and alkylaldehyde at elevated temperature and pressure. Although a very complex macromolecule, a generally accepted descriptive structure and preparation of kraft lignin is discussed in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., vol. 15, pages 280, 284-286. Also, the isolation and properties of kraft lignin are described in K. V. Sarkanen and C. H. Ludwig, Lignins, pages 838-840. Examples of commercial kraft lignin are available under the tradenames Curan manufactured by LignoTech Sweden AB (a member of the Borregaard Group) in Vargon, Sweden and Indulin manufactured by Westvaco in Charleston Heights, S.C. Kraft lignin can also be chemically modified in different ways, e.g. sulfonation, methylation, carboxylation and fractionation.
Many organic materials have been used in the prior art to improve the cycle life and low temperature capacity of storage batteries of the lead-acid type. These materials have included wood flour, lignins, ligneous materials, humins, humic acids, organic material from sulfite and sulfate liquors, and the like. These materials have been known to the trade as organic expanders because of their supposed action of expanding or increasing the sponge-like nature of the negative active material.
U.S. Pat. No. 2,371,136 describes the improvements oxylignins impart to storage batteries of the lead-acid type over the organic expanders mentioned in the above paragraph. More specifically, oxylignin type materials do not produce objectionable foaming of the electrolyte during formation of the battery, nor does the use of oxylignin result in sulfation characteristic of the negative plates during such electrical formation. Further the use of oxylignins was shown to improve the cold crank ability of the storage battery over the then prior art. The effects and advantages of the use of expanders in producing negative battery plates is discussed in Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd ed., vol. 3, page 655.
In the present invention, it has been found that both the cycle life and the cold crank ability of a storage battery of the lead-acid type can be improved beyond using the oxylignin or kraft lignin alone by incorporation of a mixture (or reaction products) of both the oxylignin and the kraft lignin. In effect there appears to be a synergy between the two materials. When used together in an appropriate blend the result is improved cycle life and cold crank ability performance beyond either when used alone.
Accordingly, the present invention provides an organic expander composition for use in a negative plate of a lead-acid storage battery. The composition comprises a blend of an oxylignin and a kraft lignin wherein the blend contains from about 1 part oxylignin and about 2 parts kraft lignin to about 2 parts oxylignin and about 1 part kraft lignin. The blend may optionally be composed of a condensation reaction product of an oxyliginin and a kraft lignin.
The oxylignin may be a condensation reaction product between oxylignins, or between an oxylignin and a kraft lignin, and condensation agent. The kraft lignin may be a condensation reaction product between kraft lignins or between a kraft lignin and an oxylignin and a condensation agent.